A modem portmanteau of modulator-demodulator is a hardware device that converts data into a format suitable for a transmission medium so that it can be transmitted from computer to computer historically over telephone wires. A modem modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted Best Data V.32bis Fax.

Best Data 336SP - fax / modem Specs

The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems Best Data V.32bis Fax be used with almost any means of transmitting analog signals from light-emitting diodes to radio. A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data.

Modems are generally classified by the maximum amount of data they can send in a given unit of timeusually expressed in bits per second symbol bit ssometimes abbreviated "bps" or bytes per second symbol B s. Modems can also be classified by their symbol ratemeasured in baud. The baud unit denotes symbols per second, or Best Data V.32bis Fax number of times per second the modem sends a new signal.

News wire services in the s used multiplex devices that satisfied the definition of a modem. Modems grew out of the need to connect teleprinters over ordinary phone lines instead of the more expensive leased lines which had previously been used for current loop —based teleprinters and automated telegraphs. Inthe Allies developed a voice encryption system called SIGSALY which used a vocoder to digitize speech, then encrypted the speech with Best Data V.32bis Fax pad and encoded the digital data as tones using frequency shift keying.

Mass-produced modems in the United States began as Best Data V.32bis Fax of the SAGE air-defense system in the year the word modem was first used [2]connecting terminals at various airbases, radar sites, and command-and-control centers to the SAGE director centers scattered around the United States and Canada.

While they ran on dedicated telephone lines, the devices at each end were no different from commercial acoustically coupled Bellbaud modems. However, the FCC's seminal Carterfone Decision ofthe FCC concluded that electronic devices could be connected to the telephone system as long as they used an acoustic coupler. Since most handsets were supplied by Western Electric and thus of a standard design, acoustic couplers were relatively easy to build.

An even lower-cost option was the Pennywhistle modemdesigned to be built using parts from electronics scrap and surplus stores. Best Data V.32bis Fax

Best Data MACH 2 - fax / modem Specs

Like the A, it used different frequency bands for transmit and receive. It was similar in design, but used the lower frequency set for transmission.

According to Vadic, the change in frequency assignments made the intentionally incompatible with acoustic coupling, thereby locking out many potential modem manufacturers. The Hush-a-Phone decision applied only to mechanical connections, but the Carterfone decision ofled to the FCC [ who?

This opened the door to direct-connect modems that plugged directly into the phone line rather than via a handset. However, the cost of passing the tests was considerable, and acoustically coupled modems remained common into the early s. The rapidly falling prices of electronics in the late s led to an increasing number of direct-connect models around In spite of being directly connected, these modems were generally operated Best Data V.32bis Fax their earlier acoustic versions — dialing and other phone-control operations were completed by Best Data V.32bis Fax, using an attached handset.

A small number of modems added the ability to automatically answer incoming calls, or automatically place an outgoing call to a single number, but even these limited features were relatively rare or limited to special models in a lineup. When more flexible solutions were needed, third party " dialers " were used to automate calling, normally using a separate serial port to communicate with the dialer, which would then control the modem through Best Data V.32bis Fax private electrical connection.

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PC Modem Init Strings

V.32bis and V.32 Modem Software

PC Modem Init Strings

V.32 and V.32bis Software Features

The introduction of microcomputer systems with internal expansion slots made the first software-controllable modems Best Data V.32bis Fax. This led to a series of popular modems for the S bus and Apple II computers that could directly dial the phone, answer incoming calls, and hang up the phone, the basic requirements of a bulletin board system BBS. The seminal CBBS was created on an S machine with a Hayes internal modem, and a number of similar systems followed.

The next major advance in modems was the Hayes Smartmodemintroduced in This allowed both data and commands to be sent through a single serial port. The now-standard Hayes command set included instructions for picking up and hanging up the phone, dialing numbers, and answering calls, among others.

F INTERNAL FAX/DATA MODEM

This was similar to the commands offered by the internal modems, but unlike them, the Smartmodem could be connected to any computer with an RS port, which was practically every microcomputer built. The introduction of the Smartmodem made communications much simpler and more easily accessed. This provided a growing market for other vendors, who licensed the Hayes patents and competed on price or by adding features.

This led to rapid growth of online services with their large file libraries, which in turn gave more reason to own a modem. The rapid update of modems led to a similar rapid increase in BBS use, which was helped by the fact that BBSs could control the modem simply by sending strings, rather than talking to a device driver that was different for every direct-connect modem. In this system, the stream of 1s and 0s in computer data is translated into sounds which can be easily sent on the phone lines.

These frequencies were chosen carefully; they are in the range that suffers minimum distortion on the phone system and are not harmonics of each other. The bit rate increases were achieved by defining four or eight distinct symbols, which allowed the encoding of two or Best Data V.32bis Fax bits per symbol instead of only 1. The use of smaller shifts had the drawback of making each symbol more vulnerable to interference, but improvements in phone line quality at the same time helped compensate for this.

Many other standards were also introduced for special purposes, commonly using a high-speed channel for receiving, and Best Data V.32bis Fax lower-speed channel for sending. One typical example was used in the French Best Data V.32bis Fax system, in which the user's terminals spent the majority of their time receiving information.